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ATN Muddy Brown Casts — ESENeph MCQ

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EasyAcute Kidney InjuryATN Muddy Brown CastsESENeph

A 55-year-old man develops AKI post-operatively after cardiac surgery. His creatinine rises from 100 to 380 umol/L. He is producing 600 mL urine/day. Urine microscopy shows muddy brown granular casts. What is the likely histological diagnosis?

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Correct answer: E — Acute tubular necrosis (ATN)

Muddy brown granular casts on urine microscopy are the hallmark of acute tubular necrosis. In the post-cardiac surgery setting, ATN occurs from a combination of ischaemia (hypoperfusion during bypass), nephrotoxins (contrast, antibiotics), and haemodynamic instability. ATN is the most common intrinsic cause of AKI in hospitalised patients. Management is supportive (optimise haemodynamics, avoid further nephrotoxins, RRT if needed). Most ATN recovers within 1-3 weeks.

Reference: KDIGO 2012 – AKI Guideline